An apparatus for producing a spun fleece or nonwoven web of stretched filaments of thermoplastic synthetic resin generally comprises a spinning head from which a curtain of the filaments emerges, a cooling chamber below the spinning head within which the filaments are quenched, a stretching nozzle below the cooling chamber and a sieve or perforated belt upon which the filaments are deposited to form the nonwoven web. A suction source can be located below the belt for drawing air through the belt and assisting in the depositing of the nonwoven web.
Apparatus of this type and for these purposes is available in various configurations. They must, however, generally satisfy two basic requirements, namely high output in terms of the spun fleece web which is produced per unit time and the maintenance of certain quality parameters of the web within narrow tolerances.
In the apparatus described in U.S. Pat. No. 4,405,297, the stretching nozzle is a gap with a comparatively large gap width, defined by a gap-forming wall which extends substantially up to the spinning head, and another wall which is inclined toward the first wall to form a wedge-shaped cooling chamber therewith and which extends to a point at which process air can be admitted.
A special fleece deposition unit is not here provided and the stretching nozzle in the form of the gap simultaneously constitutes the fleece-deposition device.
As a consequence, a relatively large gap width is required and the gap width must be adjustable up to say 45 mm in practice.
To maintain a predetermined stable operating state with the desired output, a certain process air flow rate is required. When the output is to be increased, the process air flow rate must be increased and in practice it is found that the ability to change the process air flow rate is highly limited if quality parameters of the nonwoven web are to be maintained.
In another apparatus (see DE 40 14 989 A1), the cooling chamber has a decreasing cross section in the direction of travel of the filaments and a cross section which is rectangular in horizontal section, the cooling chamber feeding into a venturi-like constriction whose narrowest part is followed by a diffuser outlet. Here as well a special fleece-deposition unit is not provided.
The venturi constriction serves as a stretching nozzle and is shaped aerodynamically in a corresponding manner. In the transition region between the cooling chamber and the stretching nozzle a free air inlet gap is provided. An effect upon the deposition of the fleece on the sieve belt was obtained by adjustable flaps in the flow passages of the apparatus. If one attempts to increase the output starting from a stable operating state, the process air flow rate must also increase here. This gives rise to problems when deterioration of the quality parameter of the spun-fleece web is to be avoided.